1. Field of the Invention
The present invention relates to a technique for controlling the position of a driving motor (e.g. a step motor) and a print head. More specifically, the invention relates to a position control technique for accurately controlling the position of a driving motor by generating timer pulses at shorter intervals than step units, and for enhancing print quality by synchronizing the drive of the print head with the control of the driving motor.
2. Description of the Related Art
An earlier position controlling device for driving motor and a print head includes a position controller for controlling the position of the driving motor by supplying the driving motor with pulse signals resulting from an interrupt, a print controller for controlling the drive of the print head by supplying the print head with pulse signals, and a central processing unit for generating interrupt signals to drive the driving motor and the print head according to interrupt request signals generated by the position controller and the print controller and governing all of the component blocks in the controllers.
The position controller includes a first timer for generating pulses at fixed intervals, a first interrupt generator for generating drive motor interrupt signals according to the pulse signals from the first timer, a control circuit for receiving the driving motor interrupt signals from the first interrupt generator and for generating corresponding interrupt request signals in a predetermined priority order and transmitting the interrupt request signals to the central processing unit, a first buffer for temporarily storing driving motor drive signals from the central processing unit, and a fire drive circuit for moving a carriage having the print head attached thereto to a desired position by controlling the driving motor according to the signals stored in the first buffer.
The print controller includes a second timer for generating pulses at fixed intervals, a second interrupt generator for generating print head interrupt signals according to the pulse signals from the second timer, the control circuit for receiving the print head interrupt signals from the second interrupt generator and for generating corresponding interrupt request signals in a predetermined priority order and transmitting the interrupt request signals to the central processing unit, a second buffer for temporarily storing print head nozzle drive signals from the central processing unit, and a second drive circuit for driving the nozzle of the print head by reading the signals stored in the second buffer to perform a printing job.
The position of the driving motor is controlled as follows. The time for one step of the driving motor is fixed in the first timer so that the first timer can output pulse signals at fixed times.
The first interrupt generator, which has received the pulse signals from the first timer, outputs interrupt signals corresponding to the pulse signals and is enabled or disabled depending on control signals from the central processing unit.
When the first interrupt generator is enabled, the pulse signals from the first timer are inputted to the control circuit via the first interrupt generator and are supplied to an interrupt terminal of the central processing unit to require an interrupt in the predetermined interrupt priority order.
The central processing unit, which received the interrupt request signals, generates an interrupt to transmit control signals for controlling the position of the driving motor to the first buffer. By data stored in the first buffer, the first drive circuit drives the driving motor and consequently, the carriage having the print head attached thereto moves.
The method in which the position of the print head is controlled is similar to the method for controlling the driving motor.
The time for moving the print head is fixed in the second timer so that the second timer can output pulse signals at fixed times.
The second interrupt generator which received the pulse signals from the second timer outputs interrupt signals to the control circuit and is enabled or disabled depending on control signals from the central processing unit.
The control circuit, which received the interrupt signals, transmits the interrupt signals received in a priority order to the central processing unit to require an interrupt.
The central processing unit, which received the interrupt signals, generates an interrupt and outputs signals for operating the print head to the second buffer.
The data stored in the second buffer is transmitted to move the print head via the second drive circuit, whereby the nozzles of the print head operate to perform a printing job.
In short, the central processing unit generates an interrupt by the interrupt request signals which are generated depending on the fixed times in the timers. Then, the driving motor and the print head are controlled to perform the printing job.
However, the earlier position controller for a driving motor and a print head has several problems. Whenever the driving motor and the print head drive, interrupts are required. In addition, two times need to be fixed in the two respective timers. One time is for the next step of the driving motor and the other time is for driving the print head. This results in an overload in the CPU during high-speed driving. An increased cost and limited control are other defects. The position of the driving motor is calculated only by the interrupt occurrence and is controlled by the step units thereof.
Accordingly, for more accurate control, a costly precise motor is required.
Furthermore, the limitation of the step angle prevents the controlling of the motor by a smaller step unit.
The following patents each disclose features in common with the present invention but do not teach or suggest the specifically recited technique for controlling the position of a driving motor and a print head in accordance with the present invention:
U.S. Pat. No. 5,527,121 to Santon, entitled Printhead Carriage Control Method And Apparatus For Achieving Increased Printer Throughput, U.S. Pat. No. 5,541,508 to Suzuki, entitled Position Detector For Synchronizing Operation Of A Recording Device With That Of A Carriage In A Recording Apparatus, U.S. Pat. No. 5,547,295 to Kanemitsu, entitled Carriage Driving Method And Apparatus For Efficiently Accelerating To A Constant Speed, U.S. Pat. No. 5,416,395 to Hiramatsu et al., entitled Carriage Drive Control For A Printer, U.S. Pat. No. 5,427,461 to Hirai et al., entitled Serial Printer With Carriage Position Control, U.S. Pat. No. 5,485,178 to Tateyama et al., entitled Printer Control Apparatus For Synchronously Controlling Driving Of Recording Head And Transfer Of Data, and U.S. Pat. No. 5,245,359 to Ito et al., entitled Recording Apparatus With Recording Head Carriage Driving Motor Control.